Commercial crude anthracene forms masses of yellowish to brown crystalline scales with an odour resembling that of naphthalene ; according to the degree of purification, it contains 30-39% of anthracene (English anthracene A con- tains 40-50%). Pure anthracene forms white, tabular crystals with a blue fluorescence m.pt. 216-5°, b.pt. 360° ; it is slightly soluble in alcohol, ether, benzine, carbon disulphide and cold benzene, and readily soluble in the hot in benzene, pyridine and glacial acetic acid. CARBOLIC ACID Crude and pure carbolic acid are on the market. The former is of some- what variable composition, the name being often given to yellowish or dark brown carbolic oils containing, besides varying quantities of neutral tar oils, also phenol and its homologues (mainly cresols), whereas it is also used to designate pale red products rich in phenols and crystallising more or less easily when cooled. The pure product is colourless or pale red, crystallisable and soluble in 15 parts of water. In very impure products the determination of the phenols and neutral oils is carried out as in 2 ; in the others, the water, solidification point, and the solubility are determined (3, 4 and 5) and, if required, the quantita- tive estimation according to Koppeschaar (see 2). 1. Characteristic Reactions of the Phenols.—The following reactions are used: (a) The aqueous solution of a phenol gives a violet coloration with dilute ferric chloride solution (provided mineral and organic acids, alcohol, ether and glycerine are absent). (b) When heated gently with a little ammonia and a few drops of sodium hypochlorite, the aqueous solution of a phenol gives an intensely blue coloration. (c) The substance is shaken with water and the aqueous solution treated with bromine water: if it is a phenol, a voluminous, white precipitate of tribromophenol, at first flocculent and afterwards crystalline, is produced. It is soluble in alkali and is reprecipitated on acidification of the alkaline solution. The tribromophenol reaction (Landolt's reaction) is sensitive to about i part in 44,000. The cresols and also other organic compounds are precipitated by bromine water. (d) A very sensitive reaction is as follows : About I c.c. of the oil to be examined is shaken with i c.c. of alcohol, after which 2 c.c. of water and i c.c. of about i% nitrazole solution (fresh) are added and again shaken : addition of a little caustic potash then colours the aqueous layer an intense red in presence of phenols. 2. Determination of Phenols and Neutral Oils.—The approximate determination of the phenols and neutral oils in crude phenol may be rapidly carried out by shaking a measured volume of the sample with double its volume of 10% sodium hydroxide solution in a stoppered graduated cylinder, allowing to stand and reading the volume of the neutral oils which separate ; subtraction of this volume from that of the substance used gives the quantity of phenols. To facilitate the separation of the neutral oils it is sometimesrystallised from alcohol in reddish-yellow needles melting at 145°.